1. Field of the Invention
The present invention relates to a nonvolatile semiconductor memory device and a manufacturing method thereof, and for example, to a nonvolatile semiconductor memory device utilizing a resistance changing layer having a resistance value changing on the basis of an applied voltage, as a memory element.
2. Description of the Related Art
As far as a memory device formed on a plane is concerned, to increase memory capacity, further miniaturization is required in order to increase the number of cells per unit area. However, the further miniaturization is not easy owing to process limitations or the like.
To increase the memory capacity without miniaturization, it is possible to stack and seal a plurality of memory chips in a package or to stack memory cell arrays on silicon to form a three-dimensional memory chip. However, the conventionally proposed method of stacking cell arrays is to simply stack conventional planar cell arrays. If planar cell arrays are stacked in a staircase pattern in a vertical direction, process costs required to form wires and contacts increase; which increase in costs exceeds the effect of high integration.
In the field of nonvolatile memories, efforts have been made to research and develop flash memories as well as ferroelectric memories (FeRAMs), MRAMs (Magnetic RAMs), OUMs (Ovonic Unified Memories), and the like.
A resistance changing nonvolatile memory (ReRAM: Resistance RAM) that is different from the above-described nonvolatile memories has recently been proposed. The ReRAM is a nonvolatile memory which allows information to be written by applying a voltage pulse to set a resistance value for a resistance changing layer in a memory cell and which allows information to be read in a nondestructive manner.
Furthermore, as a related technique of this kind, a phase changing memory has been disclosed which has basic cell arrays each comprising a plurality of memory cells formed in a horizontal direction and stacked in the vertical direction (Jpn. Pat. Appln. KOKAI Publication No. 2006-514392).